1. Field of the Invention
This invention lies in the field of alumina-based ceramics, and particularly composites of alumina and titania. This invention further relates to methods of processing metal oxide powders into ceramic materials of high density.
2. Description of the Prior Art
Composites of alumina and titania are known for their high toughness, low thermal expansion, and low thermal conductivity. These properties make alumina-titania composites desirable materials of construction and coatings for high-performance applications where thermal barriers are required. These composites are not easily formed by machining, however, and must therefore be formed by superplastic forming, for example with gas pressure or the use of dies. Superplastic forming entails high strain, however, and alumina-titania composites, like many ceramic materials, are susceptible to microcracking. The advent of nanotechnology, however, holds promise for improving the performance properties of alumina-titania ceramics, since when flaws are present in composites with nano-sized grains, the flaws tend to be smaller in size and the composite is therefore more resistant to cracking under high strain. Alumina-titania nanocomposites demonstrate superplasticity at higher strain rates than their microcrystalline counterparts. Superplasticity allows the composites to be formed to net shape in shorter processing times.
Ceramics with nano-sized grains are typically prepared by consolidation of nano-sized powders. This is particularly true of ceramics that contain two or more components, and alumina-titania ceramics are an example of such multi-component ceramics. A difficulty with conventional means of consolidation from nano-sized powders is that grain size tends to grow during the consolidation. This limits the performance of the consolidated material and the options for forming the consolidated material without creating microcracks. In addition, nano-sized powders are costly to obtain.